DESCRIPTION: This application will try to achieve the long term culture of type A spermatogonia. Three specific aims are proposed: 1) to determine the basement membrane components that are optimal for allowing long-term (longer than 1 week) survival of type A spermatogonia in culture; 2) to test the hypothesis that there is synergism between growth factors and basement membrane components in promoting long-term survival of spermatogonia; and 3) to develop immortalized cell lines of type A spermatogonia that will propagate in culture without losing their original properties.